Hi Tom,
I think the lack of uptake is because ESLs have chosen to use old/crusty style languages, rather than moving to a higher level. Why not implement an ESL in something like Ruby or Python? Using C++ to generate high-level models is not my idea of a time saver, nor is it very "fun". SystemC is only marginally better.
Additionally, I think that the IP developers are "getting it". Dillon Engineering has a rather interesting Python-based flow (http://www.dilloneng.com/ingenuity/paracore/flow) that would be nicely completed with a Python-based ESL.
Just my thoughts.
Good luck!
- Brendan